Fredholm consistency of upper-triangular operator matrices

In this paper, for given operators A is an element of B (H) and B is an element of B (K), we characterize the set of all C is an element of B (K, H) such that the operator matrix M-C = [(A)(0) (C)(B)] is Fredholm consistent. We completely describe the sets boolean AND(C is an element of B(K, H)) sigma(FC) (MC) and boolean OR(C is an element of B(K, H)) sigma(FC) (MC). Also, we prove that boolean AND(C is an element of B(K, H)) sigma(FC) (MC) = sigma(FC) (M-0).